Explants of fresh bovine and human retinal epithelium (RPE) will be maintained in organ culture. Phagocytic particles such as latex microspheres, bacteria, and isolated rod outer segments will be added to the apical surface of the RPE. Engulfment of particles will be assessed by light and electron microscopy, and when labeled particles are used, by scintillation spectroscopy. The phagocytic ability of RPE from rod-rich areas of human retina will be compared to that of cone-rich areas. RPE isolated from cattle eyes and freed of contaminants will be fractionated by sucrose density gradient or differential centrifugation. Fractions will be assayed for enzymatic markers and their organellar content identified by electron microscopy. BIBLIOGRAPHIC REFERENCES: L. Feeney and R.N. Mixon. Sulfate and Galactose Metabolism in Differentiating Ciliary Body and Iris Epithelia: Autoradiographic and Ultrastructural Studies. Invest. Ophthalmol. 14: (5) 364-379, 1975. L. Feeney, R.P. Burns, and R.N. Mixon. Human Subretinal Fluid. Its Cellular and Subcellular Components. Arch. Ophthalmol. 93: 62-69, 1975.